The code is released into public domain, which means you can freely copy it, modify and release as your own skin without providing attribution and with absolutely no restrictions.
Remember to change the license information if you do not intend to provide your changes on the same terms.

Download and place the file(s) in a directory called Example in your skins/ folder.

Add the following code at the bottom of your LocalSettings.php:

wfLoadSkin('Example');

Done - Navigate to Special:Version on your wiki to verify that the skin is successfully installed.

To users running MediaWiki 1.24 or earlier:

The instructions above describe the new way of installing skins using wfLoadSkin(), since MediaWiki 1.25. If you need to install this skin in earlier versions, instead of wfLoadSkin( 'Example' );, you need to use:

require_once"$IP/skins/Example/Example.php";

(To run a skin on an earlier release, you may need to download the version of it tagged for that release from Special:SkinDistributor.)